Bidirectional memories are memory devices that use bidirectional voltages and/or currents in order to read and/or write the state of the memory device. Bidirectional memories range from non-volatile storage devices to processor cache memory. For example, the state written to a Spin Torque Transfer (STT) magnetic memory device depends on the direction of the current flowing through the device.
Conventional bidirectional memories include at least one selector transistor per memory cell. Typically, conventional bidirectional memories include two selector transistors per memory element. Although conventional bidirectional memories may be stacked within multiple levels above the selector transistors, which are located on the die beneath the bidirectional memory, the density of such conventional bidirectional memories is limited by the area that is required for the selector transistors. That is, the sizes and the number of the selector transistors place a limit on how dense a conventional bidirectional memory may be made.